Electrical transforming system



Patented June 17, i930 UNITED STATES PATENT OFFICE m1: A. OTRLINGEB, OISHARON, PENNSYLVANIA, ASSIGNOB TO WESTINGHOUSE ELEC- TRIO &EANUFACTURJNG COMPANYFA CORPORATION OF PENNSYLVANIA EIZE C'IBJKJAL TRANSFOBMIN G SYSTEM Application tiled February 11, 1928. Serial No.253,826.

My invention relates to electrical transforming systems and moreparticularly to transformers having high voltage ungrounded rimary andsecondary win ings.

y invention resides in apparatus for changing the ratio of the voltagetransformation between the primary and secondary windings of a highvoltage ungrounded transforming system and it is characteristic of myinvention that transformers provided with equipment constructed inaccordance therewith are efiicient in operation and economical tomanufacturel It is further characterist-1c of equipment constructed inaccordance with my invention, that it may be mounted within the sametank' as the main transformer unit, thereby providing a completeassembled un t of relatively small size and cost.

Heretofore, transformers have been provided with taps to permit acertain varia- 'tion of ratio between the input and out ut voltages.These taps were usually place 1n the primary winding and were connectedto studs mounted on a terminal board. Changesin ratio were effected bymoving certain links or jumpers between the studs on the terminal board.This was a slow laborious process and required a disconnection of boththe primary and secondary windings of the transformer from the lines.

. Furthermore, the manipulation of the coni Y nections on the terminalboard had to be venience, but practically a matter of necessity toprovide some means for varyin the voltage delivered from a constant votage supply or maintaining a constant delivered voltage with a variablesupply. Examples 'of such applications are found in transformerssupplying synchronous converters and in electric furnace installations.Also,

transformers with load tap changing equipment have been used to aconsiderable extent One of the most important applications for tapchanging under load equipment is its use with transformers to form aninterconnection between two large systems or parts of systems. Thefunction in this case is to control the transfer of wattlesspowerbetween the two parts. If the voltages of two -system, to be tiedtogether at one point, tend to vary with respect to each other, thewattless transfer would vary in proportion and in many cases would beexcessive unless provisions were made to form a flexible tie-in wherebythe voltage ratio might be varied to compensate for the difference involtage between systems. Conversely, if the two system voltages shouldremain constant, changing the voltage ratio of the interconnectingtransformer would permit power factor control of the load transferred.

Tap changing equipment designed in accordance with my invention, isparticularly applicable to high voltage ungrounded transformer units andcomprises, in general, the combination of a transformer having a primaryand a secondary winding of means for changing the voltage ratio of thesaid two windings comprising a series transformer in circuitrelationwith one of said windings, and means for energizing the seriestransformer comprising a tertiary winding that is inductively related tothe primary winding. A tap changing system and a preventive autotransformer are provided for changing the magnitude and direc-,

tion of energization of the series transformer under load. i Myinvention, however, may be more readily understood if the accompanyingdrawings are referred to in connection with the following description.

The single figure of the accompanying drawings is a schematic diagram ofa single phase transformer having tap changing Itwill be understood,while I have shown.

my invention embodied in a. single phase transformer, that it is not tobe thus hmlted but that it is readily applicable to other types, forexample, polyphase transformers having their windings connected'in staror in delta.

Referring to the drawings,a tank 1 is shown housing a core 2 oflaminated. magnetizable material on which are disposed a primary winding3, a secondar winding 4 and a tertiary winding 5. Cl he primary winding3 is energized from any suitable source through conducting leads 6 and7. The difference of potential between the conducting leads 6 and 7 maybe of a high magnitlude, for example, substantially, 132 kilov0 ts.ondary win ing 4 by means of conductin leads 8 and 9. The difference ofpotentia between the conducting leads 8 and 9 is also of high magnitudefor example approximately 120 kilovolts.

It is desirable and it is the object of my invention to provide meansfor changing the ratio of transformation between the primary winding 3and the secondary winding 4 while the transforming operation is takinplace without disconnecting the circuits 0 either the whole or a portionof either the primary or the secondary winding.

To this end, I provide means for modifying the electromotive force ineither the primary or the secondary winding by means of the tertiarywindin 5.

Inaccordance wit my invention, I modify the voltage induced in thesecondary winding 4 by means of a series transformer 10 that ispreferably mounted on and built into the same unit as the maintransformer core 2.

The series transformer 10 comprises a laminated magnetizable core 11 onwhich are disposed a secondary winding 12 and a primary winding 13. Thesecondar winding4 of the main transformer is divi ed into twosubstantially equal sections 14 and 15 and the secondary windin 12 onthe series transformer 10 is pre erably connected by conducting leads 16and 17 between the two sections 14 and 15.

The series transformer 10 is energized by the tertiary winding 5 and maybe connected therewith in an suitable manner as, for example, throug apreventive auto transformer 18. The preventive auto transformer 18comprises a magnetizable core 19 having a single winding 20 disposedthereon. The winding 20 is preferably divided into two substantiallyequal sections 21 and 22. The two sections 21 and 22 are connected at ajunction point 23 to one terminal of the sec- Ener ization is takenfromthe sec-' preferably mounted within the casing 1 togather with thesenes transformer 10 therey providing a minimum number of auxiliarywindings and cores.

The tertiary winding 5 is provided with a plurality of taps 24, 25, 26,27 and 28. The tap 26 that preferably comprises the midoint' of thetertiary winding 5 is connected by a conductor 29 to the primary winding13 of the series transformer 10.

A switchin device 30 is mounted'in an auxiliary casing 31 that ispreferably secured to the transformer tank 1. This switching device maybe of any convenient form and is not to be considered a part of thisinvention. The switching device 30 has the same number of switches asthere are taps on the tertiary winding 5 and comprises, in the exampleshown, switches 32, 33, 34, 35

and 36. Each of these switches comprises two contactors A and B.Contactors Aand B may be operated to close or to open either by hand orb automatic operation. The contactors A o the switches 32, 33, 34, 35and 36 are connected by conductors 37, 38, 39, 40 and 41 tothe taps 24,25, 26, 27 and 28 of the tertiary winding 5.

The middle tap 26 of the tertiary winding 5 is connected throughconductor 29-and'the primary winding 13 of the series transformer 10 tothe junction 23 of the windings 21 and 22 of the preventive autotransformer 18. One section 22 of the preventive auto transformer 18 isconnected to the tertiary in series with the tertiary winding 5. Suchimpedance drop is almost entirely reactive and therefore its effect onregulation is practically negligible at power factors above 65 per cent.

For normal operation of the transformer, switch 34 of the switchingdevice 30 is closed. To change the taps one step to change the ratio ofvoltage transformation either switch 33 or 35 is closed. Eitheroperation places both halves of the winding of the auto transformerwinding 18 in circuit relation with the primary winding 13 of the seriestransformer 10 and the glolsition between the taps on the tertiary win g5.v

By way of explanation, suppose that the switches 34 and 35 are closed.In such case,

the auto transformer 18 is placed directly across the taps 26 and 27 ofthe tertiary winding 5. The primary winding 13 of the series transformeris connected between the midpoint 23 of the auto-transformer winding 20and the tap 26 of the tertiary winding 5. The windin 13 is excited by avoltage of a magnitude t at is equivalent to a mid-voltage on thetertiary 5 between taps 26 and 27, connected direc y to the winding 13and one side of the auto transformer 18.

To change the taps 'zinother step switch- 34 is ,opened and the full volbetween taps 26 and 27 of the tertiary 5 is used to excite the winding13,

Closing the switches controllin the ta s 26 to 28 of the tertia windin 5c an es t e voltage of the secon ary win 12 in one direction, forexample, to increase it, whereas closing the switches contro the ta s 26to 24 of the tertiar winding 5 c anges tiie voltage of thesecon arywinding 12 in the opposite" direction or in this case operates todecrease it.

When full load current is passed through I one-half of the autotransformer 18 with the other half open, the load current from thetertiar winding 5 becomes the exciting current 0 the auto transformer18. Under this condition there are no neutralizing ampere turns from theother half, so the transformer becomes a reactor. Air gaps are providedin the core to give low impedance when operating in this manner, which,of course, make the excitin current, when operating as an auto transormer across taps higher than it would be otherwise.

The switches of the tap changing device 31 are closed and "opened tochange in steps the ratio of transformation of voltage between thewindings 3 and 4. To decrease the ratio,

first switch'35 is closed; this is the first step and the voltagejratiois changed accordingly. To decrease the ratio another step the switch34is opened. For a further change of ratio the switch 36 is closed.Lastly, to change the ratio to a minimum in that direction the switch 35is opened which places the winding 13 across one-half of tertiarywinding 5 with one-half of the auto transformer winding 20 in seriescircuit relation between them.

Thesequence of operation of the switches in increasing the ratio oftransformation is in'the' other direction; that is switch 35' isclosed,-36 opened, 34 closed, 35 opened, 33

closed, 34 opened, 32 closed and 33 opened. Each time one of theswitches opens or closes the ratio of transformation is changed onestep.

A tap changing system constructed in accordance with my invention may beapplied directly to the transformer unit by virtue of the fact that noadditional separate regulating. units are required. This provides acheap, efiicient and compact equipment for effecting a change in thevoltage ratio be- -tween the windings of a high voltage transset forthboth the series and auto transformers may be mounted in the same casingas the mam transformer, thereby reducin the numberof bushings andsimplifying t e connections and installation. In the case of tapchanging equipment designed to operate on'-.

high voltage ungrounde units in accord- 'ance with my invention theauxiliary exciting winding is built into the same core and the number ofauxiliary windings and cores is therefore reduced and the overallefliciency of the apparatus is thereby materially improved.

The tertiary winding described above for exciting the seriestransformermay be used for supplying an additional low voltage cir-' cuit ifdesired.

Various changes and modifications may be made in my invention withoutdeparting from the spirit and scope thereof as set forth I ends thereof,and means comprising a tertiary winding and a series of contactorswitches for energizing said lastnamed transformer.

2. In a transformer, the combination with a primary and 'a secondarywinding, of means for changing the voltage ratio between said windingswhile under load comprising a transformer in circuit relation with oneof said windings at a point intermediate the ends thereof, and means forenergizing said last named transformer comprising a tertiary windingenergized by said primary winding.

3. A system-for changing the voltage ratio of a'power transformer underload comprising a series transformer associated with one of the windingsof the transformer and connected between substantially equal sectionsthereof, a tertiar winding energized by the primary windin of thetransformer, means for energizing the series transformer by the saidtertiary winding, anda series of contactor switches for changing themagnitude and direction'of such energization.

4. A system for changing the voltage ratio of a power transformer underload comprising a series transformer associated with one of the windingsof the transformer and connected between sections thereof, a tertiarywinding energized by the primary winding of the transformer, means forenergizing the series transformer by the said tertiary winding, andmeans for changing the magnitude and direction of such energization,said last named means comprising an impedance and circuit opening andclosing contactors in circuit relation with taps on said tertiarywinding.

with

, transformer under 1 including a series transformer for modifying 5. Atap stem for a power changing comprising means the output voltage andhaving a winding connected between sections of the main transformerwinding, means for energizing the said series transformer comprising atertiary winding in the transformer, and means for changing themagnitude of ener 'zation of the said series transformer incl'u ing atap changing device associated with said tertiary winding.

In testimony whereof, I have hereunto Subscribed my name this 3rd day ofFebruary,

KIRK A. OPLINGER.

